The invention relates to a display device of a motor vehicle and a method for operating such a display device.
Such display devices of motor vehicles and methods for operating such display devices are well known from the series production of motor vehicles, especially automobiles. FIG. 1 shows such a display device 10 according to the prior art in a schematic front view. The display device 10 is commonly also referred to as a combination instrument and is used in automobiles of the AUDI brand.
The display device 10 comprises a first display element 12 in the form of a so-called tachometer, by which values of a revolution rate of an internal combustion engine for driving the automobile can be displayed. For this the display element 12 comprises a scale of values 14 with the values for the revolution rate and a pointer 18 pivotable about a pivot axis 16 along the scale of values 14. The pointer 18 indicates the current value of the revolution rate. In the present case the internal combustion engine is turned off, so that the value of the revolution rate is 0.
The display device 10 comprises a second display element 20 in the form of a so-called speedometer, by which values of a vehicle speed of the automobile can be displayed. For this purpose the display element 20 comprises a scale of values 22 with values of the vehicle speed and a pointer 26 pivotable about a pivot axis 24 along the scale of values 22. The current value of the vehicle speed can be displayed by the pointer 26. In the present case the automobile is stationary, so that the value of the vehicle speed is 0.
The display device 10 also comprises a third display element 28 for displaying values characterizing a fill level of a fuel tank of the automobile. Moreover, a fourth display element 30 for displaying values of a temperature of a liquid coolant or a temperature of a lubricant is provided.
Furthermore, the display device 10 comprises a fifth display element 32 that is in the form of a liquid crystal display screen for displaying different values. One of said values is the current time of day 34 in the present case. Another of said values is a range 36 over which the automobile can still be driven by the internal combustion engine using an amount of fuel remaining in the fuel tank.
The display of the respective values by the display elements 12, 20, 28, 30, 32 takes place here by transmitting light beams through the respective display element 12, 20, 28, 30, 32. This means for example that the liquid crystal display screen (display element 32) transmits light beams in order to display the current time of day 34 and the range 36. Each display element 12, 20, 28, 30, 32 comprises at least one illumination element for example for transmitting the corresponding light beams.
A relevant display brightness of the respective display elements 12, 20, 28, 30, 32 can be set in order to provide pleasant brightness conditions for the driver of the automobile. In the case of bright ambient conditions, for example a high display brightness is set, whereas in the case of comparatively dark ambient conditions a lower display brightness is set.
The display device 10 (combination instrument) also comprises a detection device that cannot be seen in FIG. 1 with a control unit and at least one detecting element 38 for detecting an ambient brightness of the surroundings of the display elements 12, 20, 28, 30, 32.
Within the scope of the method for operating the display device 10, the respective display brightness is adjusted by the control unit depending on at least one signal characterizing the detected ambient brightness and transmitted by the detecting element to the control unit. The detecting element 38 is for example a photodiode or a phototransistor.
The display device 10 also comprises another detecting element 40 that cannot be seen by the driver or other vehicle occupants in the passenger compartments of the automobile and that is only illustrated in FIG. 1 in order to enable a clear explanation of its function. The other detecting element 40 is used to test the functionality of the liquid crystal display screen (display element 32). The detecting element 40 is in the form of a phototransistor here for example.
The use of the additional detecting element 40 for testing the functionality of the display element 32 requires both additional costs of development and also of wiring and installation space.
A display instrument for a motor vehicle is also known from DE 103 41 622 B3. The display element comprises an optical fiber for detecting the ambient light with a sensor that is disposed on the optical fiber and, depending on the detected ambient light, outputs a control signal for controlling the brightness of the display element to an evaluation circuit. Furthermore, a display device with an optical fiber as known can be obtained from DE 101 60 296 A1, wherein the optical fiber is mounted in the display device. An ambient brightness can be measured by the optical fiber. The brightness of the display device can then be adjusted depending on the measured ambient brightness.
DE 32 45 299 A1 also discloses a display device in motor vehicles with control of the brightness of the display device depending on the light passing from the observation space to the display. Furthermore, moreover a photodetector for detecting the light density of the surroundings in the viewing direction of the driver is provided, which adjusts the brightness of the display device depending on the light density by a control circuit.
Such display devices are also known from JP 2002071395 A and from DE 10 2009 036 316 A1.